1. Field of the Invention
The present invention relates generally to a so-called picture-in-picture type television receiver in which a sub-picture screen is inset into a main picture screen in a picture-in-picture fashion.
2. Description of the Prior Art
There is known a so-called picture-in-picture type television receiver in which a sub-picture screen is provided within a main picture screen such that pictures having different contents can be displayed on the main and sub-picture screens, respectively. According to this prior art television receiver, the television channels of the main picture and the sub-picture or the number of an external video signal input terminal are displayed on a front panel of the television receiver using a display apparatus such as an LED (light emitting diode) and the like or these numbers are displayed on the picture screen of the cathode ray tube. When these numbers, which are referred to herein as discrimination characters, are displayed on the screen, they are displayed on the main picture screen together.
Further, the picture-in-picture type television receiver is provided with a main tuner for selecting the video signal for the main picture screen and a sub-tuner for selecting a video signal for the sub-picture screen. In such a prior art television receiver, it is preferable that the channel selection operations can be carried out independently in the main and sub-tuners. Thus, the discrimination characters of the contents of picture, for example, the characters of the channels selected, are independently carried out on the main and sub-picture screens in response to the respective channel selection operations.
The assignee of the present application has previously proposed such a picture-in-picture television receiver in which each time the content of a picture displayed on the main picture screen is changed, the discrimination characters of the contents of pictures are made not only on the main picture screen but also on the sub-picture screen, respectively. This previously proposed picture-in-picture television receiver is disclosed in co-pending U.S. application Ser. No. 944,660, filed Dec. 19, 1986.
However, when the picture discrimination characters are respectively displayed on the main and sub-picture screens, the picture to be displayed on the sub-picture screen is formed such that sampling lines and picture elements of the sub-picture video signal are selected and other lines and picture elements are thrown away or removed in response to the ratio between the sizes of the main and sub-picture screens. As a result, the sub-picture discrimination character is very small on the sub-picture screen so that the discrimination character becomes difficult to see from the normal viewing distance of the user.